Quite true, but in practice there is simply not enough force to take advantage of the reduced cooldown. The primary motivation for thrash-less rotation is the lack of force. I would be interested to see if there was a rotation that:
a) kept dark ward, discharge, and wither buffs present
b) allowed more than 1 shock every 6 seconds.
It may be that by delaying wither extra force can be used to get energized procs *and* actually have the force to take advantage of the reduced cooldown. At the moment I do not see this rotation being able to generate the same or similar hps.
Thing with Shadow (and really all tank) rotations is that a reasonable portion of the resource management comes from defending and shielding attacks. Different fights are going to proc those resources at different rates. For example, resource management on Kephess or Jarg is drastically different to on Stormcaller or Zorn.
Kitru's is really the best "catchall" rotation. Thrash-less + Thrash when excess force is available. That said, in my experience I don't usually get to Thrash more than once every 2 or 3 rotations.